This invention relates to a clutch system of the friction type placed in a power transmission system. Typical clutch systems include a clutch input such as a clutch basket, a clutch output such as a center clutch, and one or more plates making up a clutch pack and disposed between the clutch input and clutch output. When the clutch pack is compressed, the clutch input and clutch output become rotationally coupled. The clutch pack is typically compressed by a pressure plate; the pressure plate typically providing a compressive force via a spring mechanism or through a centrifugally actuated mechanism.
Typically, such clutch systems include a clutch disengagement system consisting of a lever mechanically coupled to the pressure plate such that when the lever is actuated, the pressure plate's compressive force on the clutch pack is removed, disconnecting the rotational coupling between the clutch input and clutch output. Clutch disengagement systems typically couple the lever to the pressure plate mechanically through a hydraulic actuation system or a cable actuation system.
Most motorcycles incorporate a manual transmission coupled to the engine via a multi-plate clutch assembly in an oil bath. Typically, the multi-plate clutch is engaged/disengaged by the operator via a lever mounted on the handlebar. Engines with high output, require more spring pressure to transmit the torque of the engine. The operator must overcome this spring pressure at the lever to disengage the clutch. Excessive spring force can cause fatigue for the operator.
A typical multi-plate clutch system, such as the clutch system incorporated in a 2011 Honda CRF-450R uses a clutch pack incorporating 8 friction plates coupled to the clutch input and 7 driven plates coupled to the clutch output. The friction plates are 3 mm thick and the driven plates are 1.6 mm thick. By configuring the clutch with 1.8 mm thick friction plates and 1.2 mm drive plates, a clutch pack can be configured using 12 friction plates and 11 driven plates in approximately the same space. With the additional number of friction surfaces, spring force in the clutch can be reduced by ⅓ and still transfer the same amount of torque as the 8 friction plate clutch pack providing a significant benefit to the operator in terms of reduced clutch lever effort.
However, as more clutch plates are added to the clutch system, parasitic drag is increased during clutch disengagement. Parasitic drag is torque transferred between the clutch input and the clutch output when the clutch lever is in the disengaged position. Parasitic drag has many causes. One cause is the incidental contact between adjacent friction and drive plates. Another cause is inadequate distribution of oil between the friction and drive plates. Parasitic drag can make it difficult for the operator to find neutral position of the transmission at idle speed, make it difficult to change gears during operation, or cause the motorcycle to drag forward as engine speed is increased with the clutch lever disengaged.
Multi-plate clutch systems typically deliver oil to the clutch pack through two different mechanisms: by the flow oil under centrifugal force as it flows from the inside to the outside of the clutch pack or from the outside inwards as the clutch system rotates in a bath of oil, the rotation in the bath forcing oil into the plates. In many clutch system designs, there is very little oil coming from the inside of the clutch. In clutch systems that rotate in an oil bath, generally no design considerations are made to help oil flow into the clutch pack before centrifugal forces push the oil back out of the clutch pack.
Therefore a need exists for an improved friction plate design that better distributes oil between the friction and drive plates to improve lubrication and to help keep the plates separated to reduce incidental contact to reduce the effects of parasitic drag.
A preferred embodiment of the present invention is shown in FIG. 1.